Frequency multiplier of the cavity resonator type



March 13, 1951 D. R. HAMILTON FREQUENCY MULTIPLIER OF THE CAVITY RESONATOR TYPE 2 Sheets-Sheet 1 Filed Aug. 9, 1945 INVENTOR DONflLD A? HflM/LTON ATTORN EY March 1951 D R HAMILTON 2,544,675

FREQUENCY MULTIPLIER OF THE CAVITY RESONATOR TYPE Filed Aug. 9, 1945 a 2 Sheets-Sheet 2 3 INVENTOR DONALD E. HHM/LTO/V BY ,g

ATTORNEY Patented Mar. 13, 1951 FREQUENCY MULTIPLIER OF THE CAVITY RESONATOR TYPE Donald R. Hamilton, Garden city, Y., assignor to The Sperry Corporation, a, corporationof Delaware Application August 9, 1945, Serial No. 609,781 8 claims. (01. 315 -6) The present invention is directed toward the art including electron discharge devices operating in the microwave region, for example, at frequencies of the order of 300 megacycles per second and higher.

The present invention is more particularly directed toward improvements in frequency-multipliers for multiplying such microwave frequen ci es; for example, for multiplying frequencies of the order of 300 megacycles per second to values of the order of 10,000 megacycles per second or higher.

The present invention is also directed toward cavity resonator electron discharge devices for producing such frequency-multiplication.

In the prior art it has been known to use the principle of velocity modulation for periodically varying the velocities of the electrons of a uniform velocity and density electron stream at a predetermined fundamental frequency. Thereafter the varied-velocity electrons are passed through a drift space in which the faster electrons overtake the slower electrons to produce a punching or conversion of the uniform electron stream to a variable-current electron stream, also known as a density-modulated stream. This bunched or variable-current stream in the prior art may be passed through a pair of grids associated with a cavity resonator or other tuned circuit tuned to a harmonic of the predetermined fundamental frequency, for extracting energy from the stream at such a harmonic frequency. Devices of this type are shown in Hansen and Varian Patent No. 2,281,935, granted May 5, 1942.

The present invention is directed toward improvements in velocity-modulation frequencymultiplier devices of this type. The prior art devices of the type shown in the Hansen and Varian patent inherently produce low power output due to their relatively low efficiency, especially where high frequency-multiplication ratios are desired. The present invention provides novel features for increasing the efficiency and power output of devices of this type.

According to a principal feature of the present invention, three separate tuned circuits, preferably of the cavity resonator type, are caused to interact with the electron stream of the device. The first resonator is tuned substantially to the fundamental frequency to be multiplied and serves to velocity-modulate or periodically vary the velocities of the electrons of the stream. The second resonator or tuned circuit is interposedalong the path of the stream in energyinteracting relationship thereto and is separated from the velocity-modulating position of the first resonator by a drift space producing at least partial launching or conversion to varying current. This second resonator is normally floating (that is, unexcited by any external source and unconnected to any load) and is tuned substantially to a harmonic of the fundamental frequency lower than, but subharmonically related to, y the desired output frequency. The third resonator is separated from the effective position of the second resonator by a further drift space and is tuned substantially to a harmonic of the resonant frequency of the second resonator. Of course, this is also a harmonic of the fundamental frequency. Output energy is then derived from this third resonator. By the use of the second resonator, in addition to the velocitymodulating resonator and the energy-extracting resonator which were characteristic of the prior art, substantially increased power output may be derived from the stream at the output frequency. This is especially advantageous where high multiplication ratios, such as from fifteen to thirty, are desired.

Accordingly, it is an object of the present invention to provide improved electron discharge apparatus having a plurality of tuned circuits greater than two in number interacting with an electron stream, the successive tuned circuits being each harmonically related to its preceding tuned circuit.

It is another object of the present invention to provide improved frequency-multiplying apparatus of the cavity-resonator type, using a plurality of cavity resonators greater than two in number, each tuned substantially to a harmonic of the resonant frequency of the preceding resonator;

It is a further object of the present invention to provide improved electron discharge apparatus of the velocity-modulation type utilizing a tuned velocity-modulating means and a tuned energyextracting means harmonically related thereto, and utilizing an intermediate tuned circuit or cavity resonator coacting with the electron stream between the velocity-modulating and energy-extracting means and tuned to a different frequency from these means, this different frequency being integrally related to both the frequencies of the modulating and extracting means.

The invention in another of its aspects relates to novel features of the apparatus described herein for achieving the above and other objects of the invention and to novel principles employed in this apparatus, as used according to the above-mentioned objects or in the same or different fields.

A further object of the invention is to provide improved apparatus and methods embodying novel features and principles adapted for use in realizing the above objects and also in other fields. 1 Other objects and advantages of the present invention will become apparent from the specification, taken in connection with theaccompanying drawings, wherein Fig. 1 is an elevational view, partly in longitudinal cross-section, of a preferred form of the present invention;

Fig. 1A is a detail cross-section of Fig. 1 along line |A-|Athereof; and V Fig. 2 is a similar elevational view of a modi- Tied form of the present invention, using an'external tuned circuit in the first stage.

Referring to Fig. 1, a first cavity resonator II is formed by an outer conducting cylinder l2, a pair of coaxial inner cylinders I3 and M, and end pieces l6 and H. A pair of electron-permeable electrodes or grids l8 and I9, preferably of the form shown in Fig. 1A, are mounted respectively in the adjoining ends of tubes I3 and I4 and provide a narrow velocity-modulating gap therebetween. Capacity-defining members 2| and 22 are connected respectively at the ends of tubular members i3 and I4 and provide an effective lumped capacitance which reduces the physical size of the resonator II for the'desired fundamental frequency to which resonator I is substantially tuned. End wall I1 of resonator II also contains a flexible diaphragm 23 which permits relative motion between grid 18 and member 2|, on the one hand, and grid l9 and member 22, on the other hand, to permit variation or tuning of the resonant frequency of resonator A flange 24 is rigidly connected to tubular member I3, grid |8 andcapacity member 2|, and is normally urged toward the end plate IT by a plurality of compression spring members 26 symmetrically disposed about the axis of the device. The motion offiange 24 toward end plate H is opposed by a similar plurality of tuning struts or screws'Zl having lock nuts 28. It will be apparent that by turning screws 21 in either direction, a corresponding change in the separation of grids l8 and I9 is produced, thereby correspondingly altering the tuning of resonator Resonator II is provided with an input coupling loop 29 and an input terminal 3| of the coaxial type coupled thereto, to permit coupling resonator ii to a suitable source 13 of fundamental frequency energy which it is desired to multiply. By Way of example, source 13 may be a relatively low frequency crystal oscillator in combination with conventional frequency-multipliers for multiplying the oscillator frequency to a value suitable for supply to the frequency-multiplier of the present invention.

A second resonator 32 is provided, formed by an outer cylindrical wall 33, an inner concentric tubular member 34, a rigid end wall 36 interconnecting tubular members 33 and 34 and a further end wall 31 connected to the right end of tubular member 4 by a flexible wall portion or diaphragm 38. The end of tubular member l4 carries an electron-permeable electrode or grid 39, and a similar grid or electrode 4| is carried by the adjoining end of tubular member 34 to form a narrow gap therebetween. A capacity-defining member 42 cooperates with diaphragm 38 to provide capacity-loading for resonator 32, 5

mitting reduction in its physical size. Resonator 32 may similarly be tuned by adjustment of the separation of the gap between grids 39 and 4|. For this purpose a flange 43 is rigidly connected to the outer wall |2 of resonator II and is thus rigidly connected to grid 39. A second flange 44 is rigidly connected to outer wall 33 of resonator 32 and is accordingly rigidly connected to grid 4|. Flanges 43 and 44, and hence grids 39 and 4|, are urged together by a series of tension springs 46 disposed symmetrically around the axis of the device, in a fashion similar to the tuning device of resonator ll. Motion of the grids 39 and 4| toward one another is opposed by a similar series of tuning screws 4'! having lock-nuts 48, andthe tuning of resonator 32 may therefore be adjusted to a desired value by adjustment of the screws .41. Resonator 32 may be provided'with a coupling loop 49 and a coaxial line terminal 51 from which low power of the harmonic frequency to which resonator 32 is tuned may be extracted, such as for the purpose of properly adjusting its resonant frequency, as by use of a wavemeter coupled thereto. Normally, however, terminal 5| and loop 49 are not used and may be omitted, resonator 32 thereby being floating.

A third resonator 52 is provided in the path of the electron stream and spaced from the second resonator 32. Resonator 52 has a cylindrical outer wall 53 and a concentric tubular inner wall 54. A rigid end wall of resonator 52 is provided by member 36, and the other end wall is formed as a flexible wall portion or diaphragm 56 connected between cylindrical outer wall 53 and the tubular inner wall 54. Member 36 carries an electron-permeable electrode 51 concentrically thereof, which is adjacent to a similar electrode 58 mounted on the adjoining end of tubular member 54. The tuning of resonator 52 is eflected in a manner similar to that of the resonators and 32 by biasing spring means 62 and tuning screws 59 having lock-nuts 6|. The electron beam, after passing through the gap between grids 51 and 58, is suitably collected on the wall of an electron collector 63, secondary electrons being prevented from disturbing the operation of resonator 52 by a secondary-electron-suppressing grid 64.

A cathode 66 cooperates with an accelerating or smoother grid 61 mounted in member 3 to form an electron gun upon the application of a high positive potential upon grid 61 relative to cathode 66. The source of this positive potential is schematically indicated by the battery 88 connected between a base prong 69 and ground at H, cathode 66 being connected to the prong 69. The main body of the device is grounded as at 12, thereby providing a ground connection for the accelerating grid 51. The electron stream thus produced travels successively through the first resonator gap between grids I8 and I9, through the first drift space within tubular member I4, through the second resonator gap between grids 39 and 41, through the second drift space provided by tubular member 34, through the third resonator gap provided by grids 5'? and 58, and is then collected by the collector 63.

In operation, resonator II is excited at the fundamental frequency f to be multiplied by means of any suitable source connected to its terminal 3|, such as the source schematically indicated at 13. This produces a standing elec tro-magnetic field within resonator II, which sari-tat is tuned substantially to this fundamental; fre-. quency. This field produces an alternating electric field and voltage of. the fundamental fre quency between grids l8 and I9, extending axially of the stream. When the electrons of the stream pass through this field, they are alter nately accelerated and decelerated; that is, they are velocity-modulated. v

The subsequent passage of these velocitymodulated electrons through the first drift space provided by member 14 permits the faster electrons to begin to overtakethe slower electrons, and thereby produces a slight partial bunching or conversion of the velocity-modulated electrons into a varied electron current. As discussed in the above-mentioned Hansen and Varian Patent No. 2,281,935, such a varying electron current contains" current components of the fundamental frequency and'also of frequencies harmonically related thereto; that is, integral multiples of the fundamental frequency. When such a stream passes across the second gap between grids 39 and M, a standing electromagnetic field of the harmonic frequency n f (where n is an integer and f is the fundamental frequency) to which resonator 32 is substantially tuned is produced within resonator 32. This field, being produced by the electron stream, automatically builds itself up in such a phase relation relative to the alternating current component of the electron current of frequency nxf so as to be in phase opposition thereto; that is, the alternating voltage appearing between grids 39 and 4| is in such a sense and has such a phase that when the partially formed electron bunches pass across the second gap, they experience a maximum retarding effect. This action, when followed by passage through the second drift space defined by member 34, results in the electrons of the bunches being concentrated more highly, which in turn produces a higher energy content in the varyingcurrent electron stream at frequencies which are harmonics both of the fundamental frequency and of the harmonic frequency of resonator 32. Accordingly, by the time this varying currentelectron stream passes through the third ap between grids '51 and 58, "the enhanced bunching has taken place so that a greater amount of powercan be extracted from the electron stream by the third resonator 52 tuned substantially to a harmonic p of the resonant frequency of the second resonator 32. This output power of frequency P n f may be extracted from the resonator 52 by means of a coupling loop 74 and is supplied through an output terminal 16 to any suitable load or utilization device Hf Another embodiment of the invention operating in accordance with the same principles discussed above is shown in Fig. 2, where the same reference numerals, but primed, are used to indicate corresponding structures. In the embodiment of Fig. 2, the first resonator II is replaced by an external tuned circuit I I. For this purpose grid I9 is fixed to the grounded metal envelope of the tube. The adjacent grid I8 is completely insulated from the metallic envelope. Connected between grids l9 and I8 is an input tuned circuit II, to which is coupled the source 13 of fundamental frequency f. It is to be understood that any suitable type of tuned circuit, such as formed by lumped inductance and capacitance or by a transmission line, may be used as tuned circuit ll'.

Resonators 32 and 52' correspond exactly to resonators 32 and 52 of Fig. 1. Thus, resonator 32' has a pair of grids 39' and Ill separated from grids l8 and H) by a first drift space formed tubular member l4. Resonator 52' has a pair of grids 51 and 58' separated from grids 39 and 4| by a second drift space defined by tubular member 34'. Resonators 32" and 52' may be tuned in a manner similar to that described with respect to Fig. l.

In operation, tuned circuit H is again substantially tuned to the input fundamental frequency f. Resonator 32' is tuned substantially to the harmonic frequency nxf. Resonator 52' is tuned substantially to a harmonic of the frequency of resonator 32, that is, to a frequency pxnxf. The operation of the device of Fig. 2 is the same as that'of Fig. 1, and greater amounts of output energy of the frequency p n may be derived, as discussed relative to Fig. 1.

While the embodiments of the invention illustrated in Figs. 1 and 2 use three tuned circuits or cavity resonators, it will be understood that the present invention contemplates the use of more than three such circuits, where desirable, the essential relationship being that each such circuit shall have a resonant frequency which is substantially an integral multiple of the resonant frequency of the resonator next adjacent to it toward the cathode.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Ultra high frequency apparatus comprising means for producing an electron stream, a first cavity resonator along the path of said stream and in velocity-modulating relationship thereto, a second cavity resonator along the path of said stream in energy-exchanging relationship thereto and spaced from said first resonator, means defining afield-free space surrounding the path ofsaid stream between said first and second resonators, a third cavity resonator along the path of said stream in energy-extracting relation thereto and spaced from said second resonator,

andmeans defining a field-free drift space surroundin the path of said stream between said second and third resonators, said first and second space-defining means having a length sufficient to cause the velocity-modulated electron stream to attain substantially maximum bunching at said third cavity resonator, said second resonator being tuned substantially to a harmonic of the resonant frequency of said first resonator and said third resonator being tuned substantially to a harmonic of the resonant frequency of said second resonator.

2. High frequency apparatus comprising means for producing an electron stream. three cavity resonators positioned successively along the path of said stream, the first of said resonators having a frequency characteristic including a fundamental frequency and further being tuned to said fundamental frequency, the second of said resonators being maintained in a floating condition and havin a frequency characteristic including a frequency harmonically related to said fundamental frequency and further being tuned harmonic frequency and further being tunedto said frequency harmonically related to said harmonic frequency, and means for extracting energy from said third resonator.

3. Ultra high frequency apparatus comprising means for producing 'a stream of electrons, three cavity resonators positioned successively along the path of said stream in energy-exchanging relationship thereto, means coupled to the first of said resonators for supplying fundamental frequency energy thereto, said second resonator being floating and tuned substantially to a harmonic of said fundamental frequency,and said third resonator being tun-ed substantially to a harmonic of said fundamental frequencywhich is also substantially a harmonic of said firstnamed harmonic frequency.

4. High frequency apparatus comprising means for producin an electron stream, three pairs of electron-permeable electrodes positioned successively along the path of said stream, the electrodes of each of said pairs being closely juxtaposed to one another to provide narrow gaps therebetween, a cavity resonator coupled to the second of said electrode pairs, a second cavity resonator coupled to the third of said electrode pairs, means coupling a source of fundamental frequency to said first electrode pair, said first resonator being floating and tuned substantially to a harmonic of said fundamental frequency, and said second resonator being tuned substantially to a harmonic of said harmonic frequency, and a load coupled to said second resonator. 5. High frequency apparatus comprising means for producing an electron stream, means along the path of said stream for velocity modulating the electrons thereof at a fundamental frequency, means along the path of said stream spaced from said velocity-modulating means for extracting energy from said stream at a harmonic of said fundamental frequency, and a floating cavity resonator positioned along the path of said stream between said velocity-modulatin means and said energy-extracting means and tuned substantially to a frequency which is a harmonic of said fundamental frequency and a subharmonic of said first-mentioned harmonic frequency. 1

6. Ultra-high-frequency apparatus comprising means for producing a stream of electrons, three cavity resonators positioned successively along the path of said stream in energy-exchanging relationship thereto, means coupled to the first or said'iesonators for supplying fundamental frequency energy thereto, said second resonator being floating and having a resonant frequency substantially equal to a harmonic of said fundamental frequency, said third resonator having a resonant frequency substantially equal to v a harmonic of said frequency of said second resonator.

7. High frequency apparatus comprising means for producing an electron stream, a first velocitymodulating cavity resonator positioned along the path of said electron stream, said resonator having a frequency characteristic including a fundamental frequency, a second velocity-modulating cavity resonator along the path of said stream, said second cavity resonator being maintained in a floating condition and excited only by said stream and having a frequency characteristic including a first frequency harmonically related to said fundamental frequency, a fieldfree drift space located intermediate said first and second resonators, a third energy-extracting cavity resonator along the path of said stream, said third resonator having a frequency characteristic including a second frequency harmonically related to said first harmonic frequency, and a field-free drift space located between said second and third cavity resonators. 8. Apparatus as in claim '7, wherein said first cavity resonator is further tuned to said fundamental frequency, said second cavity resonator is further tuned to said first harmonically-related frequency and said third cavity resonator is further tuned to said second harmonically-related frequency.

DONALD R. HAMILTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

